Figure 1812

Estimation of protein catabolism and nitrogen balance. The extent of protein catabolism can be assessed by calculating the urea nitrogen appearance rate (UNA), because virtually all nitrogen arising from amino acids liberated during protein degradation is converted to urea. Besides urea in urine (UUN), nitrogen losses in other body fluids (eg, gastrointestinal, choledochal) must be added to any change in the urea pool. When the UNA rate is multiplied by 6.25, it can be converted to protein equivalents. With known nitrogen intake from the parenteral or enteral nutrition, nitrogen balance can be estimated from the UNA calculation.